Yuko Ishibashi

Potentiometric flow injection determination of manganese(II) by using a hexacyanoferrate(III)–hexacyanoferrate(II) potential buffer

A highly sensitive potentiometric flow injection analysis method for the determination of manganese(II), utilizing a redox reaction with hexacyanoferrate(III) in near neutral media containing ammonium citrate is described. The analytical method is based on the detection of the change in potential of a flow-through type redox electrode detector, resulting from the composition change of an [Fe(CN)(6)](3-)-[Fe(CN)(6)](4-) potential buffer solution. A linear relationship between the potential change (peak height) and the concentration of manganese(II) was found. Manganese(II) in a wide concentration range from 10(-4) to 10(-7) M could be determined by appropriately altering the concentration of the potential buffer from 10(-3) to 10(-5) M. The lower detection limit of manganese(II) was determined to be 1x10(-7) M. The sampling rate and relative standard deviation were 20 h(-1) and 1.9% (n=8) for 6x10(-6) M manganese(II), respectively. The proposed method was successfully applied to the determination of manganese(II) in actual soil samples obtained from tea fields. Analytical results obtained by the proposed method were in good agreement with those obtained by an atomic absorption spectrophotometric method.

Change in Manganese Concentrations in a Small, Tea Field River Catchment and Characteristic of Manganese Elution from Soil on Tea Field

Manganese concentrations and pH in a small, tea field river catchment were measured in 1998 and 2015. The pH levels dropped between May and June of 1998, but in 2015 there were few changes throughout the year. This difference is hypothesized to have been due to reduced fertilizer use between April and July and improved fertilization methods. While manganese concentrations were consistently lower in 2015, further investigations of manganese loading are required. Furthermore, a comparison of field soil and forest soil indicates that one factor leading to high manganese concentrations observed in a small river was a corresponding high concentration in tea field soils; additional factors include significant water-soluble components, exchangeable ions, and the exposure of carbonates, which are soluble in weak acids.